A federal judge ruled Wednesday that BP PLC and one of its minority partners in the blown-out Macondo well are liable for civil penalties under the Clean Water Act for their roles in the nation’s worst offshore oil spill. U.S. District Judge Carl Barbier also ruled that Deepwater Horizon rig owner Transocean Ltd. may be liable under the same law as an “operator” of the well. The judge, however, said he couldn’t decide before a trial scheduled to start Feb. 27 whether Transocean meets the definition of that term. The Justice Department argued that BP, minority partner Anadarko Petroleum Corp. and Transocean are each liable for per-barrel civil penalties for oil discharged from the well. Barbier rejected Anadarko’s argument that oil discharged from Transocean’s rig, not the well. “Pressure within the earth drove hydrocarbons up the Macondo Well, through the (blowout preventer), and finally out the riser,” the judge wrote.

“Thus, the uncontrolled movement of oil began in the well. The riser and (blowout preventer), by contrast, were merely passive conduits through which oil flowed.” Barbier also ruled that BP and Anadarko – but not Transocean – are “responsible parties” under the Oil Pollution Act for oil that flowed from beneath the surface of the water.